The diacetylene group, --C.tbd.C--C.tbd.C--, is a highly reactive functionality that, in the correct solid-state geometry, can be topochemically polymerized using heat, chemical radicals, or radiation into a fully conjugated polymer with extensive pi-electron delocalization along its main chain backbone. See Wegner, G. (1979) "MOLECULAR METALS", W. E. Hatfield, ed., Plenum Press, New York and London, 209-242. Since the polymerization is topochemical, the kinetics of the reaction and the structure of the final product can be directly attributed to the geometric arrangement of the reacting groups in the solid-state. See Baughman, R. H., J. POLYM. SCI. POLYM. PHYS. ED., 12, 1511 (1974).
The fully extended unsaturated backbone of the polydiacetylenes gives rise to many of the novel properties of these materials, such as their highly anisotropic optical, electrical, dielectric, and mechanical properties. In particular, polydiacetylenes have been found to exhibit large nonlinear optical susceptibilities comparable to inorganic semiconductors, making them attractive materials for optical signal processing. See Muller, H., Eckhardt, C. J., Chance, R. R., and Baughman, R. H., CHEM. PHYS. LETT., 50, 22 (1979). This is a direct consequence of the strong variations in the polarizability of the backbone which result from the one-dimensional nature of this system. Also, in some cases, it is possible to prepare large area nearly defect-free single crystals of polydiacetylenes which offer unique optical properties. See Baughman, R. H., Yee, K. C., J. POLYM. SCI. MARCROMOL. REV., 13, 219 (1978).
The vast majority of diacetylene monomers that have been prepared and polymerized are relatively small molecules which readily crystallize from melt or solution. Generally, monomers in which a diacetylene group is flanked on both sides with various organic substituents have received the most amount of attention.
By varying the composition of these organic substituents, it is possible to obtain a wide variety of polydiacetylenes with a range of physical properties. For example, Patel et al. reported the synthesis of soluble polydiacetylenes obtained by incorporating bulky side groups with the structure, --(CH.sub.2).sub.n --OCONHCH.sub.2 COOC.sub.4 H.sub.9 (n=3 or 4), in the monomer. See Patel, G. N., Chance, R. R., and Witt, J. D., J. CHEM. PHY, 70, 4387 (1979). Here, dissolution was encouraged by an increase in the entropy content of the polymer brought about by surrounding the conjugated backbone with these flexible bulky sidegroups. Molecular weight determinations on these and other soluble polydiacetylenes indicate the average molecular weights to be around 10.sup.5 -10.sup.6 g/m. See Patel, G. N., Walsh, E. K., J. POLYM. SCI. POLYM. LETT. 17, 203 (1979); Wegner, G., and Wenz, G., MOL. CRYST. LIQ. CRYST., 96, 99-108 (1983).
Surface active polydiacetylenes have also been prepared by fitting the diacetylene monomer with a hydrophobic "tail" group on one side of the molecule and a hydrophilic "head" group on the other. See Tieke, B., Lieser, G., and Wegner, G., J. POLYM. SCI. POLYM. CHEM. ED., 17, 1631-1644 (1979). Such monomers can be manipulated at the air-water interface of a Langmuir-Blodgett film balance and subsequently polymerized into a polymer monolayer. This technique is currently being used to fabricate controlled thickness multilayers of polydiacetylenes suitable as optical waveguides. See Garter, G. M., Chen, Y. J., and Tripathy, S. K., APPL. PHYS. LETT., 43, 891 (1983). The polymerization of the diacetylene groups is believed to proceed via a 1, 4 addition polymerization. Wegner, G., MOLECULAR METALS, 209-242 (Plenum Press, 1979).
In addition to the polymerization of monomeric diacetylenes, it has been demonstrated that the diacetylene functionality can be incorporated in the repeat structure of a polymer backbone. These types of polymers undergo solid-state cross-polymerization on exposure to U.V. radiation forming polydiacetylenes chains.
These materials have been referred to as macromonomers due to the systematic polymerization of the diacetylene units within the backbone structure of the initial polymer giving rise to a final network-like structure consisting of polymer chains both normal and parallel to the original chain direction. The term cross-polymerized is used to indicate that polymer chains are formed at regular intervals along the original polymer backbone as opposed to the typical random cross-linking that many polymers undergo when exposed to radiation. Examples of polymers containing the reactive diacetylene functionality in the repeat structure of the polymer backbone include polyurethane and polyester polymers formed by linking the appropriate difunctional monomers together and wherein one of which contains the diacetylene group. See Wegner, G., DIE MAKROMOLEKULARE CHEMIE, 134, 219-229 (1970). Alternatively, it has been found that these polymers can be synthesized by the oxidative coupling of terminal diacetylenes. See Hay, A. S., Bolon, D. A., Leimer, K. R., and Clark, R. F. POLYMER LETTERS 8, 97-99 (1970). Using this chemistry, Hay et al. prepared polymers based upon bispropargyl ethers of bisphenols which incorporate the diacetylene unit as part of their repeat structure. In addition, using similar chemistry, polymers of the type (--(CH.sub.2).sub.n --C.tbd.C--C.tbd.C--).sub.x have been prepared. See Day, D. and Lando, J., J. POLYM. SCI., POLYM. LETT. ED., 19, 227 (1981); Thakur, M. and Lando, J., MACROMOLECULES, 16, NO. 1, 143 (1983). In this case, it was shown that the polymers undergo a systematic cross-polymerization via the diacetylene unit to produce network-like polymers.
Polydiacetylenes have also been described which exhibit thermochromic properties. The term "thermochromic" as used herein refers to a reversible color change upon heating or cooling which is observed for many of the polydiacetylenes. It can not be predicted whether or not a diacetylene will polymerize. Furthermore, if the diacetylene does polymerize, it is not possible to predict whether or not the polydiacetylene produced will exhibit reversible thermochromic properties. See, "Polydiacetvlenes" Advances in Polymer Science, Cantow, H. J. Ed., 63 (Springer Verlag ed., Berlin, Heidelberg 1984).
The usefulness of the thermochromic polydiacetylenes which do exhibit reversible thermochromic properties has been limited due to the fact that they exhibit a hysteresis effect. A polydiacetylene exhibits a hysteresis effect when the material, after it has been heated to induce the desired color change above the thermochromic transition temperature, must be cooled below and, in some cases, substantially below the thermochromic transition temperature, to a temperature designated the "hysteresis transition temperature" whereupon the original color reappears. See U.S. Pat. No. 4,215,208, Yee et al. 1980.